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Is wheel well overheat detection (not brake temperature sensor) necessary for commercial jet aircraft?
Some aircraft do have this detection system (many Boeing aircraft), some do not. Why? What's the main purpose of the wheel well temperature detection system, even though there are brake temperature sensors.

What's the main purpose of this detection system even there are brake temperature sensors.

Far more often than not, the need for brake temperature sensors is after landing to tell you how hot the brakes are. If you had to use heavy braking upon landing, they're going to be hot. How hot they are tells the captain in part how he needs to taxi and whether he should advise ground personnel to stay away from the sides of the tires where the thermal plgus are and possibly to use cooling equipment (typically a huffer) to cool them down.
Wheel well temperature sensors are needed after takeoff. The potential problem here is that you need to keep an eye on how warm the wheel well is getting from the hot tires you have retracted and enclosed in the wheel well.
As an example, let's say you have a 747 freighter loaded to a max takeoff weight of 825,000 lbs or more at Honolulu and taking off on RWY 8R. That's 20,000 feet of taxiing and another 10,000 feet plus of takeoff roll. The flexing of the tires during that taxi and takeoff generates a lot of heat. Once the wheels are in the wells, that heat transfers into the wells and eventually leaves the airplane. However, if for whatever reason, the tires already had a lot of extra heat before the taxi started or a lot of braking was done during the taxi, or the airplane was stuck down low in warmer air after takeoff, whatever, the wheel well temperature might exceed the safe limit.
The solution is usually simple, drop the gear and cool the tires. If you don't you risk a wheel well fire.

Some aircraft do have this detection system (many Boeing aircraft), some do not. Why?

The short answer is that they have been designed so that they don't need it, which begs the question: why aren't all aircraft designed such that they don't need it. Essentially every aircraft design includes compromises. It's all part of tailoring the design to best accomplish what the aircraft's primary task is to be. Using the 747 example, you could, for example, install a cooling system in the wheel wells to take care of the heat, or you could use heavier tires that didn't flex as much and thus didn't heat up as much, or you could have additional structure able to resist the heat or dissipate it quicker. But whatever means you used, it would mean hauling around more weight and the attendant costs in fuel and loss of payload capability when you didn't need it most of the time. Far better to avoid those high costs, but in the interests of safety install a much lighter system that will alert you to the need to cool off the wheel well by dropping the gear.
Insofar as potential 747 wheel well overheats are concerned, baring mechanical failure, it's generally a problem only when the aircraft is used in a manner that it wasn't designed for. For example, the 747 was designed as a long-haul transport. As such, there would be plenty of time for the wheels to cool down in the wheel wells. As I remember we were told in ground school that 5.5 hours was the cool down time. So, if you have a short leg and then a quick turn with high weights, you might be taking off with tires that have more heat in them than the system was designed to handle.
When JAL decided to use the 747 for high-density, short hauls within Japan, Boeing came up with the 747SR (Short Range) which included a redesign of the undercarriage as well as several other things. The design goal was that that any commuter airliner needs: short legs, frequent takeoffs and landings, and it made sense to optimize the design for that criteria, and that optimization required a decrease in range and payload as I remember.

Here's an accident that killed 247 people due to a wheel well fire: https://en.m.wikipedia.org/wiki/Nigeria_Airways_Flight_2120

Might that be part of the reason, when I jumpseated on an empty DC-10 from EWR to JFK we climbed to over 10,000 feet and flew most of the way down Long Island before turning around for the approach?

@TomMcW I'm not familiar with the DC-10, but given that you were empty, I doubt that tire heat would have been a problem. Also, had it been, rather than spend extra time in the air, it would be more cost effective just to drop the gear to cool things down. My guess would be that the extended flight along Long Island was just ATC sequencing you.

Cargo, engine and wheel well fire detection is considered essential for many a/c. If a high friction wheel assy. Is taken up into the enclosed environment of a wheel well any ensuing fire would be directly under the pax. Compartment a simple loop detection sys. would enable the crew to lower the gear before catastrophic failure.

Considered essential by who?

The problem isn't so much "directly under the pax" as it is "directly under the fuel tank(s)", which tend to be between the wheel well and the passengers...


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Do intermeshing rotor helicopters have a swasplate? If no, then how do cyclic and collective controls work?
Looking at the Kaman K-Max and H-43 Huskie, it looks like they rely entirely on rotor flaps. How are they controlled?

What's missing from the picture is the hydraulic actuators that move the swash plate. The K-max and all other Kaman helicopters have cyclic and collective control via servo-tabs behind the trailing edge of the blades. These can be deflected manually. The servo tabs are visible on this picture:

Further info from this site, which also shows a cutaway drawing revealing the thin control rods inside the rotor hub fairing:

The servo flap is a small airfoil located at about 75 percent span of the rotor blade, situated on the trailing edge of each rotor blade. These flaps are controlled by the pilot through push-pull control rods and their function is similar to that of an elevator on fixed wing airplanes. Moving the trailing edge of the flap upward moves the leading edge of the main rotor blade up. This increases the rotor pitch or the lift in very much the same manner as the elevator, on a fixed wing aircraft, changes the angle of attack on the wing. Thus the helicopter pilot can cause the angle of attack of the flap to increase or decrease in pitch, causing the helicopter to alternately dive or climb.

Hi Koyovis, thanks. I understood how collective control works, but I still don't understand how cyclic control works. Is there a swashplate which tilts the rotors forward/backward, and sideways?

@TonyStark the control rods are rotating and they need to be cyclically extended, so I expect that somewhere inside is an arrangement similar to a swashplate.

The first synchropter (Flettner 282 Kolibri) did have swashplates for collective pitch control. (Source: John Watkinson, The Art of the Helicopter).

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How do I compute thrust of a rotor disk and the necessary power to drive it??
as it seems, this question has been asked a few times here so please forgive me for asking again.
If I have 50 BHP shaft power available at 5000 RPM and 106 N.m torque, then can I convert it to 200 kgf of thrust?
I intend to use two sets of horizontal rotors, dividing 50 BHP between them and each generating 100 kgf thrust. Is it doable? What will be the diameter of propellers and their RPM to achieve this goal? What about pitch?
Any help, even if in part or help in the form of guidance to correct resource will be immensely helpful.
Thanks in advance :)
Edit:
1. I intend to provide vertical thrust and not horizontal as we do in aircraft.
2. I want to specifically know following things:-
Suppose I have a generic 2000 mm diameter rotor blade, (I have no idea what typical pitch value is). I want to know what RPM it needs to be turned at to produce 100 Kgf force and what will be the power or torque requirement.

You are going to lose some (or a lot) of power in the mechanism you use to divide the power between the props.

What RPM will you be turning the blades at?  If you're thinking 5000RPM, you'll need a very small diameter to keep the tips subsonic.  If you're thinking less, then you'll need a gearbox mechanism (with losses)

5000 rpm are 523,6 rad/sec and 523,6 rad/sec x 106 N.m is 55,5 kW, around 75 hp, not 50...

@xxavier yes, max torque is usually at a lower than max rpm.

What is the design speed of the craft? Horizontal rotors or vertical propellers?

Design speed? Well its main function is to hover over a point, anything that's not too bad will do it as far as horizontal speed is concerned. The rotors are horizontal i.e. parallel to the airframe.

I'm answering the question of after the Edit. Simple momentum theory:
$$ T = C_T \cdot \rho \cdot A \cdot \Omega^2 \cdot R^2 \tag{Thrust}$$
$$ P = C_P \cdot \rho \cdot A \cdot \Omega^3 \cdot R^3 \tag{Power}$$
$$ C_P = \frac{{C_T}^{3/2}}{\sqrt2} \tag{Ideal Power}$$
$$ FM = \frac{Ideal Power}{InducedPower+ProfilePower} \tag{FigureOfMerit} $$
The Figure Of Merit is a dimensional unit and provides an efficiency measure. It always gives a better result for higher disk loadings, but does provide a correction for real life effects on the ideal power. So for your case of two rotors, each with: $$ A = 3.14 m^2, \rho = 1.225, T = 981 N $$ the ideal power is:
$$P_{ideal} = N_{rotors} \cdot \left(\frac{(T)^{3/2}}{\sqrt{2 \cdot \rho \cdot A}}\right) = 2 \cdot \left(\frac{(981)^{3/2}}{\sqrt{2 \cdot 1.225 \cdot 3.14}} \right) = 22.2 kW $$
From J. Gordon Leishman, Principles of Helicopter Aerodynamics:

$$C_T = \frac{T}{\rho \cdot A \cdot \Omega^2 \cdot R^2} \tag{CT}$$
Tip speed $V_{tip} = \Omega \cdot R$ should not exceed critical Mach = 0.7 * 340 m/s = 238 m/s. At this tip speed, $C_T$ = (981)/(1.225 * 3.14 * 238$^2$) = 0.0045. Corresponding Figure of Merit = 0.55. So the power to drive both rotors would be $$22.2 kW / 0.55 = 40.3 kW$$
The rotors would turn at 238 rad/s = 2,270 rpm, hopefully that is around the rpm for max. torque for your engine. Otherwise you need to gear up/down as required, you have gearboxes anyway.
You would need to add transmission losses for driving the two rotors from your engine. Prouty gives a power loss per stage of 0.0025[max.power + actual power]. Each disk has 2 stages, so a power loss of about 0.005 * 2 * 40,283 = 0.403 kW.
$$Torque = P / \Omega = 40,685 / 238 = 170.9 Nm$$

EDIT
A numerical error in calculating $C_T$ = 0.0045 not 0.009, so the FM is lower and torque may not be enough. In that case the rotor diameter should be reduced and the rpm increased.

EDIT2
Clarified that Ideal power and Thrust coefficient are being calculated for two rotors/disks with half the load each.
original question asked for 100kg (981N) thrust each rotor, or 200kg total. So Ideal power increases from 7.8kW to 22.2kW.
$C_T$ was already calculated for each disk at 981N.

This is unbelievable, I can't really thank you enough kind stranger from the internet. Now I am going to study this momentum theory and see for myself how's and why's of its application in this case. Thank you very much again :)

No worries mate. The momentum theory is only the beginning, it gets head spinningly complex later in the books. But this is kind of a quick Order Of Magnitude computation.

Use this formula:

(From Wikipedia entry https://en.wikipedia.org/wiki/Disk_loading). Where P is the power in watts, T the thrust in Newtons, A the disk area of the rotor in sq. meters, and rho the air density in Kg/m3, around 1,22...

I would upvote this answer if it used the equation for a worked out solution.

The OP needs only to solve for A in order to know the disk area he needs, assuming 100% prop and transmission efficiency. Then he can split the area in two parts, one for each prop, and get the prop diameter. Very elementary, 12-year old algebra...

Where is profile drag and induced drag in this equation? The huger the rotor disk, the lower the power required to drive it at a given thrust?

It's a simplified approach based on momentum theory. Setting a convenient value for prop efficiency would take things closer to reality. Yes, in general, the larger the rotor disk, the lower the power needed for a given thrust. That's the reason helicopters have big rotors...

Well if I work this out with T= 981 N, area = pi sq. mtrs, density = 1.225 kg/m^3. Then it works out to Power = 981*((981/3.14)(1/(21.225)))^(1/2) = 11077 Watts, and I have 25 KW available per shaft, this looks quite promising. Assuming props are 80% efficient then it's 13.843 KW, assuming 5% mechanical losses then it's 14.572 KW. This looks magical

@Tony Stark You'd need a reduction gear, lest the tips of your 2-m diameter props go supersonic. Besides, props rarely are 80% efficient. A value of 50% is more realistic... And you should insert a more reasonable value for the mechanical losses... 20-30% will be about right...

@xxavier Assuming worst case of 50% prop efficiency and 30% mechanical losses (although there is no reason for that because there will be only a reduction drive and a couple of CV joints in between), it works out to nearly 32 KW, then it will be an engineering exercise to improve propeller efficiency, reduce mechanical losses and reduce airframe weight. I just want to check with pros here if it's feasible in the sense of not violating physics. I never expected it to be easy piesy install and fly exercise.

@Tony Stark A helicopter is a very difficult thing... Good luck...

@Xxavier thanks man, I am thankful for the time you spent helping me. I will keep coming back here to ask more questions.

@Tony Stark  Let me suggest you join the Rotary Wing Forum... You'll find it easily in the internet. There are some top-notch rotary-wing experts there...

@xxavier sure, I am doing it right away.

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Why is the minimum for VFR 1000/3 while there are VFR weather minimums for every single airspace?
It seems like I have a concept error here. I don't understand why "the VFR min is 1000/3" when I think I would need to check in which airspace I am to then check for its respective weather min corresponding to that airspace, so why bother saying 1000/3? (I am new in the community and trying to learn, apologize for entry level question)
Also, for example for class C airspace, the VFR weather mins are visibility 3sm and clouds 500 below, 1000 above, 2000 horizontal. "Above" means that clouds should be at least a distance away 1000' above the aircraft, is that what it means?
Finally, I read several websites but couldn't find if these weather minimums for each airspace are talking about only SCT and BKN ceilings or do they apply to OVC too? is it legal then to fly VFR and overcast?

When you read the "above/below" clearances, start them off with "I need to be...", for example in 2000/500 below/1000 above, you read that as "I need to be 2000 feet from (laterally), 500 feet below, and 1000 feet above clouds"...

got it that is useful, could you please help me out with the 1st and second paragraph of my question.

I'm not sure what the 1000/3 refers to, are you talking about cloud clearances and visibility? Where do you see that written?

Related; and this question may help too

This question is also related

91.155(a) sets the VFR minima for the various classes of airspace in general. Note that “1000ft above” means the plane must be 1000ft above the cloud, not vice versa as you wrote. Also, the visibility here is flight visibility.
91.155(c) adds the additional requirement of a 1000ft ceiling within the lateral boundaries of controlled airspace designated to the surface for an airport.
91.155(d) adds the additional requirement of 3 miles ground visibility within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport.
91.155(c) seems moot at first glance, since 91.155(a) requires you to stay at least 500ft below the ceiling in class C, D and E airspace and 91.119(c) requires flying at least 500ft above the ground, but 91.155(c) prevents you from using the “Except when necessary for takeoff or landing” clause of 91.119 or the “open water or sparsely populated areas” clause of 91.119(c) as a loophole. It also prevents you from using the “clear of clouds” requirement in class B from flying VFR with a ceiling of 500-999ft.
The regulations don’t give an official reason why they are written the way they are, but there is a reason we say “the rules are written in blood.” For any given regulation, think about how you are likely to die if you break it, and you will probably find at least one matching accident in the NTSB archives.
Finally, for ceiling, we find in 1.1:

Ceiling means the height above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as “broken”, “overcast”, or “obscuration”, and not classified as “thin” or “partial”.

Ok Im getting it more now. However, the fact that there is (I supposing) one ceiling only, shouldn't be necessary only to talk about 500' below ( I need to be 500 below the ceiling) how does it make sense to add another condition of "I need to be 1000' above clouds when there is supposed to be no clouds under the ceiling altitude right? thats is why is the ceiling, I am guessing.

@YamchaAviator 91.155(a) refers to any cloud, not just the ceiling layer (if there even is one). It’s legal to fly VFR above or between cloud layers, and you can fly up or down through holes as long as you can maintain the proper clearance in all directions, which is unlikely if the layer is BKN or OVC.

I don't understand why "the VFR min is 1000/3"

If someone is telling you that "the VFR min is 1000/3", then your confusion is warranted. For example, in the daytime in sparsely populated areas in Class G airspace there's no requirement that the ceiling (if present) be 1000' or higher, and you only need 1 mile visibility.

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Are there any ICAO restrictions on naming a taxiway?
According to ICAO are there any certain restrictions to naming a taxiway? For example:

a certain letter cannot be used
it cannot have letters that match a parking stand etc.

Related: https://aviation.stackexchange.com/questions/66845/why-are-oscar-india-and-x-ray-o-i-and-x-not-used-as-taxiway-identifiers

Per the Runway Safety HANDBOOK, First Edition 2014:

2.4 Taxiway Naming Convention
A simple and logical method for designating the taxiways should be developed. The following general guidelines should be followed:

Naming of the taxiways begins on one side of the aerodrome and carries on to the other extremity (e.g. from east to west or from north to south);
The letters I, O and Z are not used, in order to avoid confusion with the numbers 1, 0 and 2. Neither is the letter X used, because it is used to
indicate closure of portions of taxiway or runway;
There can be no duplication of the use of a taxiway name;
A taxiway crossing a runway should be named differently on the two sides of the runway. However, some aerodromes designate crossing taxiways with high traffic volume using the same name on both side of the runway (FAA recommendation); and
Number and letter combinations should not result in confusion with runway designations. E.g., if an airport has a runway “4L,” a taxiway designation of “L4” should not be used.
ACI recommends that a taxiway accessing a runway should be identified by a code consisting of a letter followed by a figure (e.g. A1, A2, A3 ... A12), beginning with 1 but not 0, from the extremity of the runway and continuing without missing a number.
As far as practicable, this type of identification is not used for other, less critical parts of the aerodrome: only one letter is used. The goal of this practice is to warn a pilot or a vehicle driver of proximity with a runway

As it says "general guidelines", they are not absolute rules, but recommendations.
Another source of useful taxiway information is the Certification Specifications (CS) and Guidance Material (GM) for Aerodromes Design CS-ADR-DSN. However, while it is very full of very specific information on how to make taxiways (turn radius', width, centerline, markings, shape, etc) it does not speak to naming them at all (that I could see at a skim).

My airport violates four out of the five guidelines in one way or another...

For reference since your question was specifically ICAO, the FAA has released supplemental guidance in Engineering Brief 89A (superseding EB 89) that is being used throughout the US for planning purposes.
Webpage: https://www.faa.gov/airports/engineering/engineering_briefs/eb_89
Actual Brief: https://www.faa.gov/sites/faa.gov/files/eb_89A_TWY_Nomenclature.pdf

Hi Jeff - welcome to Av.SE!  Is there a link you can edit into your answer for the new EB 89A? That would help those who want to follow up on your suggestion. Thanks for contributing, and please do come back often!


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To operate on Mars, how large would a manned helicopter's rotor blades have to be?
I asked this question at https://space.stackexchange.com/questions/53931/manned-helicopter-on-mars but there was disagreement over whether a (now deleted) answer was correct, so I've re-asked it here.
To operate a helicopter on Mars capable of carrying people, how big would the rotor blades have to be compared to a helicopter on Earth?

Manned is kind of ambiguous, is the only purpose to lift a single person? A group of people? Cargo? How far? How high?

You should not cross-post the same question https://meta.stackexchange.com/questions/64068/is-cross-posting-a-question-on-multiple-stack-exchange-sites-permitted-if-the-qu

@Ron Beyer For the sake of being specific let's say 4 people to travel 100 miles and back before refuelling and high enough to travel over most terrain on Mars but not mountains.

Perhaps a bit ambitious, nothing wrong with that in theory.  Travel on Mars is like Earth at 100,000 feet with 1/3 the Gravity.  This is why robotic airscouts and human ground transport might work better.

Your question focuses on the size of the rotor. Do you care about the power?  A full-size, speed increased rotor on mars will be supersonic.  That will generate lift, but the power requirements go through the roof.  You might be able to design a rotor that could lift humans, but not anything that could power it.

@BowlORed Yes I'm interested in anything about the feasibility. Thanks for mentioning power.

Ingenuity rotors need to rotate 5x (M 0.7) faster on Mars than on Earth.
5x faster rpm translates roughly to 25 times more lift (V$^2$).  Martian atmosphere is 1/100 pressure of Earth.  Gravity is 38% of Earth.
But Martian atmosphere is CO2, which has a 52% higher molecular weight than Earth N2/O2 mix.

0.38 gravity = 25x more lift × 1/100 density × 1.52 g/mole

Martian (and high altitude Earth flight) is possible with batteries or any propulsion source not requiring atmospheric O2.
So, to answer your question, your rotors need to be of 25x greater area, or spin 5x faster, or a combination of both, to lift an equal amount of mass on Mars.

+1. I had a go at answering on the Space site, very entertaining exercise.

+1. "CO2, which has a 52% higher molecular weight" shouldn't that be based on volumetric mass (density) and take viscosity into account?

@mins they already have rated pressure. Pressure plus molecular mass give effective density. What should also be factored in is temperature, simply because the atmosphere behaves funny when at -120C, as this is actually below the freezing point of the air's main constituent, and it's really only the enthalpy of sublimation that is keeping most of the CO2 as a gas!

@mins I was thinking of the effect of lighter water vapor on density altitude.  Same pressure, but less lift.  Before Ingenuity ever flew, I had hoped the heavier CO2 would give it more mass to flail against.

It hurts my head to think about the many factors involved! But you may be delighted by Numerical And Experimental Aerodynamic Investigation Of A Micro-UAV For Flying On Mars and Low Reynolds Number Airfoil Evaluation for the Mars Helicopter Rotor or Predicting Aerodynamic Performance for a Mars Helicopter Rotor

@RobertDiGiovanni the lift is produced by mass flow, kg/sec. Best way is to compute how much gas mass per volume of atmosphere, then momentum theory has some simplified insights in how much thrust is generated.

@mins Entertaining read, the Swedish prediction.

Not a good idea to let rotors rotate 5x faster on Mars, they already have tip speeds of M0.8 here on earth, since that is where the most gain in lift can be found. Best to increase the rotor size and retain the tip speed.

@Koyovis: In addition sound speed on Mars seems to average to only 240 m/s (at -63°C).

On the Space site it was determined that a manned helicopter flying on Mars would look like a Sikorsky Firefly with the rotor of the Mi-26. How much power would it require to drive that rotor, and would the co-axial configuration offer any benefits?

Power
The Mi-26 has 17,000 kW engine power installed to lift MTOW of 56,000 kg. A Firefly has an MTOW of 930 kg = 9100 N on Earth, 3460 N on Mars. Let's allow an additional 100 Mars kilo's for the larger number of longer blades: MTOW 4500 N.
From this answer: $$C_T = \frac{T}{\rho A (\Omega R)^2}$$ and with $\rho$ = 0.015, A = (52.5 * 31.7) = 1,664 m$^2$, $\Omega R$ = M0.8 = 250 m/s (at -31 °C), I get $$C_T = \frac{4500}{0.015 \cdot 1,664 \cdot 250^2} = 0.0029$$ This corresponds with a $C_P$ of about 0.00028, and substituting that in the power equation of the earlier mentioned answer results in P = 109 kW. The Firefly has got 140 kW on board, so will be able to power this machine with no probs!

Co-axial
On Mars, we need 31.7 times the rotor area that would be required on Earth. Yes a single rotor requires the least amount of power to drive it, but the FireFly has more power than we require for the single rotor.
If we use a co-axial rotor set-up, we don't need to drive a tail rotor and each rotor can be of a size that we have experience with on Earth, half of 1,664 = 832 m$^2$, a blade length of $\sqrt{832/\pi}$ = 16.3 m. Indeed the blade length of the Mi-26, and we only need 2 blades per rotor now.
Power to drive the co-ax rotor according to momentum theory is also given in Leishman equation 2.160: measurements have shown an increase of 22% of power required = 1.22 * 109 = 133 kW, still within the installed power of 140 kW.


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Do I need a ferry permit for an alternator repair ferry flight within a mode C veil?
My Cessna 172 SP's alternator died while stationed at a class D airport, less than 10 miles from my home field (another class D). Both airports are within the mode C veil of a nearby B airport.
Assuming that I fully charge my battery before flying to my home field for repairs, it seems to me that I can do so in full compliance with regulations. I'll fly VFR during the day, and plan to only keep my beacon (anti-collision), transponder, ADS-B out and one radio online, and shut down all other electrical equipment to make double sure my battery will have plenty enough for the flight. I'll also carry a battery-operated backup radio just in case.
My question is: am I right in assuming that I'd be perfectly legal taking this short flight? Or do I need a ferry permit from my local FSDO?

No A&P able to travel to the aircraft?

That's a bad idea, even if it's legal, deep-draining a battery is a good way to ruin it and cost you more money. If you're so close to your home base it shouldn't be hard to get an A&P to replace it

A&Ps are in short supplies around here, and not lacking for work at all. So traveling to a plane is a deal breaker for most if not all of them; I've had no luck finding any so far.

And it's less than 10 miles flying, but it's on the other side of a lake, with a big city in the middle, driving. Usually 40-50 mins with traffic, so my usual A&P isn't too keen on making the trip.

Welcome to aviation.SE! I think the real question here isn't about the mode C veil, it's whether a C172 with an inop alternator is airworthy.

@Pondlife I do think the mode C is relevant. If it wasn't for that, I would only need the beacon to be legal, and use the backup radio for comms; so I wouldn't really think twice about it.

ATC can issue you a clearance or waiver, call them up and explain what you need to do, chances are you'll be told to go ahead but coordinate with them.

@user4867444 Well, if the alternator is required for the aircraft to be airworthy then you'll need a ferry permit in any case. That's why I'd start with that question and go from there.

@Pondlife fair enough :) C172s don't have any KOEL or minimum equipment list, so the only thing that applies for day VFR flights is the old ATOMATOFLAMES. As long as the beacon is on (anti-collision), it doesn't need anything electrical on to be legal.

@user4867444 Some C172S models do have a KOEL, and it lists the alternator as required for day VFR. Yours may not, of course.

@Pondlife I stand corrected, my bad. Just double-checked mine's POH though, no KOEL.

If you don’t have a working alternator I don’t see how the airplane is airworthy. You can mark some things as inop, but I can’t imagine that an alternator would be one of them. §91.7 (a) No person may operate a civil aircraft unless it is in an airworthy condition.

@JScarry how do you come to that conclusion? What if the fuel will run out before the battery does? Many planes do not have alternators and simply charge their battery on the ground, e.g. aerobatic planes where the weight is considered a liability.

@KennSebesta The plane was certified with an alternator. Not having a working alternator would mean that it doesn't conform to it’s type certificate—hence unairworthy. Unless there is a KOEL that says that you can fly without it, my default assumption is that it’s required. If anything bad happened on the flight §91.13   Careless or reckless operation. would probably apply too.

@JScarry I see your point. Since we know it's not on the MEL and there is no KOEL, then these do not limit the poster. In the absence of those two lists, https://resources.savvyaviation.com//wp-content/uploads/articles_eaa/EAA_2011-09_too-broken-to-fly.pdf gives a very good breakdown of determining which equipment is necessary to be considered airworthy. https://aviation.stackexchange.com/questions/72207/is-it-illegal-to-fly-a-cessna-172s-under-day-vfr-with-an-inoperative-vacuum-gaug asks a similar question.

This might also be relevant to understanding whether the specific plane in question is airworthy with an inop alternator: http://www.aviationattorney.com/publications/lawfully-operating-%E2%80%9Cunairworthy%E2%80%9D-aircraft

@KennSebesta I don’t think the autopilot issue is on point. Mike Busch does point out that “If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with Part 43 of this chapter;” so if you can persuade an A&P to sign off on a faulty alternator or remove it before flight then I suppose you would be satisfying the letter of the FARs. I’m fairly certain that my A&Ps wouldn’t sign off on that without figuring out why the alternator wasn‘t working. Was it really the alternator, something else in the circuit, the gears?

No, you do not need a ferry permit to fly without the transponder[*]. If you wish to fly inside the Mode C veil, it is sufficient to reach out to ATC and ask for permission. For a 10 minute flight that stays low to the ground, I'm sure they'll be happy to help. It makes it easier on them if you can fly when they aren't slammed, but since you're not in their airspace, they are pretty understanding.
You might be surprised by the number of transponder-less aircraft flying under the Mode C veil: lots of old planes which never had electrical systems, lots of new ultralights, and there could even be gliders around. You won't be the only one up there without ADSB-Out.
FWIW, I expect that your plane can fly quite some distance with everything off but the transponder. They typically consume 10-20W, so you should have several hours' worth of energy.
[*] In general flight without an alternator might not be allowed, though. This depends on the Comprehensive Equipment List, or Minimum Equipment List, or Kinds of Operation Equipment List, or basic certification standards in effect when the plane was certified. If the alternator for your specific plane is on one of those lists as required equipment then the plane would be considered not airworthy and would require a ferry permit.


text:
What airspeed is required at sea level to create the same aerodynamic pressure as cruise altitude?
I would like to know what speed would be required, at sea level, to exert the same aerodynamic pressure as experienced at cruise altitude.
For example, if an airliner were traveling at 500kn at 35,000' what speed would you travel at sea level to experience the same forces on the air frame?

You are looking for the equivalent airspeed. Here is the definition from Wikipedia:

Equivalent airspeed (EAS) is calibrated airspeed (CAS) corrected for the compressibility of air at a non-trivial Mach number. It is also the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft is flying.

$$ \text{EAS} = \text{TAS} \times \sqrt{\frac{\text{density at altitude}}{\text{density at standard sea level}}} $$

At standard sea level, EAS is the same as calibrated airspeed (CAS) and true airspeed (TAS). At any other altitude, EAS may be obtained from CAS by correcting for compressibility error.

Assuming you mean 500 kts True Airspeed, it's whatever the indicated/calibrated airspeed shows (what the pilot sees on the airspeed tape), because that's based on the actual dynamic pressure at altitude.  Using any TAS calculator to work it backwards, a true airspeed of 500 kts is 243 kts indicated on a standard day (15C and 29.92" at sea level), so the dynamic pressure the airplane "feels" at 35000 feet is equivalent 243 kts True Airspeed at sea level.


text:
If ATC doesn't assign an obstacle departure procedure in an IFR clearance, what should you do?
If ATC doesn't assign an obstacle departure procedure (ODP) as part of an IFR clearance can you use one anyway?
And if there is no ODP, do you then follow the 35ft at runway threshold / 400ft at first turn / 200ft/nm rule, then turn on course on your own?

I believe this is a duplicate of:  https://aviation.stackexchange.com/questions/1081/when-should-an-obstacle-departure-procedure-odp-be-used?rq=1

Welcome to aviation.SE! I've edited your question a little because I think it's only about ODPs, not SIDs. If I'm wrong then of course please edit again to clarify what you're asking.

To answer your question directly, yes you can use the ODP to depart an airfield regardless of if ATC has specifically given it to you. You may use it until you reach the prescribed altitude in your IFR clearance or the beginning of the cleared routing. However, if ATC has given you specific instructions for your departure, you have to either accept those instructions and follow them. Or, decline the clearance and ask for what you need. After all, you are the Pilot in Command solely responsible for the safety of your own flight.
That being said, I have never heard an IFR clearance where the departure procedure is not explicitly spelled out. It does not have to be in the form of an official charted Obstacle Departure Procedure or complex instructions. As a matter of fact, it is usually a fairly simple instruction in order to put you in a position for ATC Departure to pick you up on Radar. It should sound like this:

C - Cleared to [your destination]
R - Fly runway heading. Radar vectors to the [blank] departure. Then as filed.
A - Altitude 3000 [or so]. Expect 10,000 in 10 minutes.
F - [Frequency you will use for departure].
T - Squawk [transponder code].

The “fly runway heading” statement means that you will fly the course of the extended center line of the runway of departure. And, continue to do so until told otherwise by ATC.
They may replace that statement with “Upon departure, turn right [blank] heading. This generally means you have the leeway to begin your turn once you are beyond the traffic pattern and/or above 1000 feet AGL.
If they stipulate for you to make an immediate turn to a specific heading as practical, do so as soon as you are above a safe altitude to bank the aircraft. I would generally make the turn when I have reached the Departure End of the Runway and above 400 feet AGL. ATC may give you an altitude at which to make that turn. In which case, make the turn at that altitude regardless of if you have reached the DER or not. Typically, ATC will not have you make the turn lower than 400 feet AGL. They would deem this as the practicable altitude for a turn. In an emergency or urgent situation, ATC may request a turn as low as 200 feet AGL. They would not want you banking low and slow in IMC.
If ATC does not give you a specific set of departure procedure instructions, the FAA recommends in the AIM that Part 91 flights should follow the charted ODP if one is available. This is only a recommendation and not a requirement. I would highly recommend informing ATC if you plan to amend their clearance instructions by departing on the ODP.
Something you may want to consider is that the numbers you alluded to in your questions are bare minimum performance values for certification of a Departure Procedure. You, as the PIC, should not be following these numbers. If your aircraft can not achieve 35 feet AGL way before the DER, and a climb rate of 200 feet per Nautical Mile, you probably should not be flying that aircraft, at that airfield, on that day, in those conditions (weight, weather, etc).
Below are the FAA recommendations for this found in the Aeronautical Information Manual Chapter 5-2-9:

a. Instrument departure procedures are preplanned instrument flight rule (IFR) procedures which provide obstruction clearance from the terminal area to the appropriate en route structure. There are two types of DPs, Obstacle Departure Procedures (ODP), printed either textually or graphically, and Standard Instrument Departures (SID), always printed graphically. All DPs, either textual or graphic may be designed using either conventional or RNAV criteria. RNAV procedures will have RNAV printed in the title; for example, SHEAD TWO DEPARTURE (RNAV). ODPs provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC. Graphic ODPs will have (OBSTACLE) printed in the procedure title; for example, GEYSR THREE DEPARTURE (OBSTACLE), or, CROWN ONE DEPARTURE (RNAV) (OBSTACLE). Standard Instrument Departures are air traffic control (ATC) procedures printed for pilot/controller use in graphic form to provide obstruction clearance and a transition from the terminal area to the appropriate en route structure. SIDs are primarily designed for system enhancement and to reduce pilot/controller workload. ATC clearance must be received prior to flying a SID. All DPs provide the pilot with a way to depart the airport and transition to the en route structure safely.
e. What criteria is used to provide obstruction clearance during departure?

Unless specified otherwise, required obstacle clearance for all departures, including diverse, is based on the pilot crossing the departure end of the runway at least 35 feet above the departure end of runway elevation, climbing to 400 feet above the departure end of runway elevation before making the initial turn, and maintaining a minimum climb gradient of 200 feet per nautical mile (FPNM), unless required to level off by a crossing restriction, until the minimum IFR altitude. A greater climb gradient may be specified in the DP to clear obstacles or to achieve an ATC crossing restriction. If an initial turn higher than 400 feet above the departure end of runway elevation is specified in the DP, the turn should be commenced at the higher altitude. If a turn is specified at a fix, the turn must be made at that fix. Fixes may have minimum and/or maximum crossing altitudes that must be adhered to prior to passing the fix. In rare instances, obstacles that exist on the extended runway centerline may make an “early turn” more desirable than proceeding straight ahead. In these cases, the published departure instructions will include the language “turn left(right) as soon as practicable.” These departures will also include a ceiling and visibility minimum of at least 300 and 1. Pilots encountering one of these DPs should preplan the climb out to gain altitude and begin the turn as quickly as possible within the bounds of safe operating practices and operating limitations. This type of departure procedure is being phased out.

Note: “Practical” or “feasible” may exist in some existing departure text instead of “practicable.”

One small clarification: fly runway heading means exactly that; fly the heading, not the runway centerline over the ground.


text:
Who has more power? Air Force One PIC or ICAO or FAA?
So, ICAO(or FAA) Controls everything in the air, but is Air Force One on top of it, or does Air Force One need to follow the ICAO's (or FAA's) regulations?

Do you suppose Air Force One would mind crashing into a B777 while over the Atlantic, outside of radar coverage?  I suppose they would be on a preplanned flight and following all the rules everyone else followed,  As far as over US territory is concerned, they file a flight plan like everyone else.

I believe Air Force One would be considered a "state aircraft" under the Chicago Convention, which means it would not be subject to ordinary ICAO regulations for civil aviation, just the general undertaking that it operate with "due regard" for the safety of civil aircraft. Of course, not being subject to the regulations doesn't mean that they won't generally comply with them in the interest of safety or that military regulations don't apply.

Related

The more interesting question would probably be asking not about Air Force One (as Terry pointed out, a military aircraft), but about Executive One.

@aCVn Considering the FAA is part of the Department of Transportation - an executive department - I suspect Executive One still wins, considering that the President can simply issue an Executive Order to the FAA telling them to do what he wants.

First, ICAO has no authority over aircraft movement in and of itself. It's a United Nations agency that, as Wikipedia puts it "codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth." Individual sovereign nations accept whatever they want of what ICAO codifies, and it is the governing aviation authority of the individual nation that has the power.
Now, in the U.S., military aviation is not governed by the FAA, the civilian agency that for the most part complies with ICAO recommendations as do most countries. However, the U.S, government has a common air traffic control system for both military and civilian aircraft. If, for no good reason, an aircraft violates the air traffic rules, the FAA will deal with that for civilian aircraft, the military for military aircraft.
Air Force One is a military aircraft. Further, as @Zach Lipton has pointed out, it is a "state aircraft." Further, whichever airplane is carrying the President of the United States is designated Air Force One (or Marine One or Navy One) only when carrying the President, and the President is the Commander-in Chief of the military. I don't know how all that sorts out, but practical considerations dictate a general adherence to the "rules of the road" so to speak.
And finally, it's accepted practice that the captain of an aircraft is the final authority aboard the aircraft for the operation of the aircraft, regardless of who is aboard.
Better to rule by consensus than by diktat if there's time for consensus.

I'd also point out that the first rule any good leader - political, business or military - should take to heart is "Unless there is an emergency, the rules apply to me as much as they do to anyone else. If I have time to ask myself if the current situation counts as an emergency, it doesn't count as an emergency."

So technically, the pilot of Air Force One can overrule the President of the United States... I can just imagine how that conversation goes. Instead of "I changed my mind, let's go to Bahamas." "Anything you like, you're the President.", we'd get "I changed my mind, let's go to Bahamas." "Sorry Sir, no. We can't do that safely.".

@aCVn Sometimes it is good to say no even to a big boss from the US government https://en.wikipedia.org/wiki/1996_Croatia_USAF_CT-43_crash (This is not to say there was any insistance on landing in this particular case, but if there is one in a dangerous situation it may better to not land even if a VIP on board gets very annoyed).

@aCVn If changing the destination to the Bahamas was somehow unsafe, then yes. If it could be accomplished safely, then no, at least that's how I understand it. In cockpit resource management training they used to put us through scenarios where someone of superior overall authority (owner of the airline) ordered the captain to do something to see how you'd handle it. I always felt those exercises were of limited value, but they did cause us to think a little.

"in the U.S., military aviation is not governed by the FAA..."  Not true, we are absolutely bound by FAA regulations, and can be issued a flight violation just like a civilian pilot.  Just like active duty military groundlings are compelled to follow traffic laws on the highway.

Indeed, if the requested change of destination could be accomplished safely, then the PIC wouldn't have that authority to fall back on. Most likely other arguments could be made, but those wouldn't necessarily (or rather, would likely not) be the PIC's to make.

@Shadur I especially like that first rule. Not quite the same seriousness, but I was once in line in full uniform for security screening in Sao Paulo, several places back from the x-ray machine. One of the screeners saw me and motioned for me to jump the line. I declined saying that I was not operating but flying as a passenger. A businessman and frequent flier behind me, accustomed to the high-handedness of Brazilian airline captains, complimented me on my action.

@aCVn Hmm... In the case of Air Force One, I suppose the President could simply issue an Executive Order to the Captain. Including one making himself Captain, if he so desired. If the Captain resisted, I suspect the Presidential Protection detail on board would side with the President (unless they believed the President to be incapacitated or some such thing.)

As the 2010 Polish Air Force Tu-154 crash show, even when the cockpit is full of VIP, the PIC should have the guts to be PIC.Unrelated persons in the cockpit trying to overrule the PIC probably was a part of the reasons a major part of the Polish top were killed.

"In the case of Air Force One, I suppose the President could simply issue an Executive Order to the Captain. Including one making himself Captain, if he so desired."  Response:  Very well sir, I relinquish command of the aircraft.  You have the controls.

@Terry I appreciate that. The airline industry is one of the few places where uniformed employees frequently cut lines in front of their paying customers (as opposed to having alternate entrances or procedures for staff) in a way that would be entirely unacceptable in most businesses.

The PIC is always the final authority for operating his aircraft. That said, pilots will follow ATC instructions when able and advise when unable. This includes miltitary aircraft in civil airspace. (The military have their own rules in their own airspace--and in combat, of course.)
AF1 is not particularly special in terms of regulations; they just won't accept ATC clearances or instructions they don't like, whereas other aircraft are expected to take what they get unless they're legitimately unable to comply. In a sense, AF1 always gets the priority handling that others only get after declaring an emergency, but how that priority works isn't any different. I don't know whether there is an actual regulation documenting that or it's just tribal knowledge within ATC; the latter would be entirely reasonable given it's just one plane.

"they just won't accept ATC clearances or instructions they don't like"  is that pretty common ?!

@Fattie For AF1?  Not too common since ATC usually asks them what clearance they want and then gives it to them verbatim.  There are occasional glitches, but it's not like anyone in ATC isn't aware of AF1's special status.

authors: Vladimir F Героям слава


text:
Why does an airplane captain sit in the left seat?
For almost every airline, the captain sits in the left seat, and the first officer on the right.

We know that in most countries right-side traffic and some have left-side.
During training, the student sits in the left seat, and the trainer on the right.

Keeping these two points in mind, why does the captain always sits on left? It is not based on culture (see #1 above), and not on who has more experience1 to fly an airplane from both seats.

1: I know that there can be a situation when the first officer is more experienced than the captain, but most of the time, it is not the case.

I don't see how you could deduce "not based on culture" from #1. Are you aware that cars produced for right-side traffic traditionally do have the driver sitting on the left side (for better line of sight)?

There are several reasons, mostly historical, or theories behind this:

After World War I, most airplanes had rotary engines with left turning tendencies because it followed the torque of the engine. Therefore, turning left was easier than turning right. Because of this, pilots considered left turns as more convenient maneuver, and thus more experienced pilot started sitting on the left.
Since the early days of aviation, the fact that pilot was sitting on the left, they keep the airplane on the right side along the airway. At that time, pilots often navigate visually following roads and railways. Opposite traffic following the same path then pass each other on the left.
Because captain sits on the left, left-hand traffic patterns are more common.
In order to avoid a head-on collision, each airplane must turn right. Since the captain sits on the left, they will have an unrestricted view of the other airplane, and therefore can assess the situation easily.

In modern times, almost all airplanes (other than single-pilot airplanes or where one pilot sits behind the other), both seats have full controls to fly the airplane.
Regulations do not specify which seat should be occupied by the pilot-in-command (PIC) or the Pilot Flying (PF).
Please note that on many helicopters, captains sit on the right side.

Bibliography:

Why a Captain sits on the left side of a plane?
Why Does The Captain Sit On The Left?
Why Captain sits on the Left?

Also the tiller is on the left side, and only captains may taxi

Not to be a bother, but the 2nd, 3rd and 4th points are all, quite likely, results of the PIC being on the left, not the original reason that the PIC ended up on the left.  The first reason, though, sounds interesting.  Though I can't help but wonder if perhaps being on the left has something to do with aviation starting in France and the US, both of which employ(ed) left hand drive in cars and carriages...

Steve Richie (USAF fighter ace in Vietnam) in an episode of Dogfights, said (paraphrasing) "I was surprised he turned right because pilots like to turn left. It's easier to do this [push stick left] than this [pull stick right]."  That makes total sense to me because I'm right handed.

"altering course to Starboard" to avoid a head on collision pre-dates aircraft altogether - perhaps early commercial flight adopted it from existing best practice - SOLAS regulations governing shipping  - along with existing standards for navigation lights. Thus point 4 might drive the PIC's seating location rather than the other way around.

I recall reading that since left turns are easier (due to point one above) most approaches were done along the runway with a left turn for final approach. Sitting on the left then gave the optimum view of the airfield before landing.

In a lot of airplanes (especially the older ones) the pilot sat in the middle.
When airframes got bigger, they also got bigger (or more) engines. In the propeller era this also produced a tendency to turn to one side easier than the other, so the drivers found turning that way to be easier (or no choice if you had a problem). If you are sitting in the middle it doesn't matter, if you have to choose a side you want the turn-toward side so you can see the ground.
A big design factor is most of us are right-hand dominant. If you have a 2-seat flight deck in side-by-side arrangement you probably want one set of common controls ( power, prop, mixture, radios etc. ) and the pilot would want to operate them with their dominant hand. You don't need precision control of the stick at the same time you are adjusting the engine or tuning the radio.
Also consider that the USA was a major player in aircraft design, and they drive on the right side of the road. Back then the pilot was king, the copilot was a trainee, management buys what the pilot tells them to buy, and the pilot will sit on the left because that's the same place he sits in his car.
Once that pattern started we end up being stuck with it. If the pilot sits on the left, they will park with the airport gate on the left and thus the doors are on the left. The next plane on the design board better follow the same conventions, because planes don't have reverse and airports didn't have tugs back then. Next we build jetways to hook up to the left side door, and now passenger cabin design expects the front left door to be the primary entrance - the front right door might not get opened for months.
Helicopters seat the pilot on the right for exactly the same reason - the pilot is probably right-handed. In a helicopter, the cyclic needs constant, precise input. You typically can't let go of it, ever1. But the collective doesn't require constant attention, and in a 2-seater can be a shared control (mechanically simpler and lighter). The pilot accepts more difficult use of the radios etc. so he can keep it flying right side up.

1: In Terminator 2, the T-1000 grows an extra hand in order to fly a helicopter while reloading his weapons. Someone on the effects team did their homework.

A couple of things things: a) controllable-pitch props were certainly around by the days of the DC-3 (which meant you could taxi backwards if you needed to if you had such a gadget on your plane) and b) my understanding is that the front right door is opened routinely for service trucks, etal to access the aircraft.

One more thing; chopper control layouts with the collective (aka the throttle) on the left were borrowed from fighter designs which are throttle-left to allow the same precision control of the aircraft with the dominant hand. So, if an ex-fighter jock turned civvie pilot wanted to sit on the right hand side to put the throttle on his left, there's quite a bit of logic behind that decision, too, provided he still had access to his instruments (on larger airliners, controls are fully duplicated; stock setup of most small craft is all about the left-hand seat).

@UnrecognizedFallingObject you want to try a powerback in a DC-3? With another one in front of you? Zero rear visibility, a tailwheel in wheelbarrow configuration and steering designed for the other direction? I want to watch.

@UnrecognizedFallingObject controllable pitch propellers are not the same thing as a propeller which allows reverse thrust. I have never seen anything suggesting that a DC-3 has the capability you suggest. Some radial-engines seaplanes of the time did have reverse thrust.

@egid -- interesting -- I thought that CPPs allowed reverse, but I wonder if the early models only supported feathering

Many don't even feather. A single with a constant speed just goes from coarse to fine.

Should be noted that A) Not all airplanes are commercial airliners that require airport gates and the like; and B) There's at least one popular line of airplanes (Piper Cherokees &c) in which the only door is on the right side, which I've always assumed is so that you can let a passenger out without getting out yourself.

What is the reference of this answer ?

they drive on the right side of the road (same reason, going back to wagons in the frontier days). << They drive on the right now, following Henry Ford and the Model-T, but in the frontier days they drove on the left with the driver on the right - watch any Wild West film.

In WWI the first European air forces were recruited from cavalry regiments. Largely because flying had been a rich man's hobby and cavalry regiments were mostly recruited by the rich (because they had previously supplied their own horses).
Horse mounted right handed soldiers wear their sword on their left side. To mount a horse with a sword hanging down your left leg  you need to mount from the left (to swing your right leg over) so they naturally mounted their aircraft from the same side.
The Royal Air Force also does't have the rank of sergeant for the same reason. Sergeant originally meant servant (so much has changed...) and a cavalry soldier  was a gentleman who would object to such a low title so cavalry regiments don't have the rank of sergeant. When the cavalry became fliers they took the same tradition with them.

The RAF certainly does have the rank of Sergeant.  http://www.raf.mod.uk/organisation/ranks.cfm

AIUI ... the first international air service was from London to Paris in 1919. The pilots used to navigate by following the railway line (the invention of IFR ). But one day, in poor weather, the outbound flight met the inbound flight in a mid-air collision, because both were flying over the railway line. So an agreement was reached that they would fly to one side of the railway line (and any other line feature being used for tracking). But which side - well the maritime rule for avoiding head-on collisions is to go right (starboard) and so they decided to go with this rule. This then led to the Captain being on the left, to be able to see the line while following it.


text:
Is there a modern day "replacement" for the de Havilland Beaver?
Is there a modern day equivalent or replacement for the Beaver's Payload, STOL and floats capabilities? By replacement, I mean that it can fly into the same airstrips under the same weather with the same load.
Is there any modern (still manufactured) airframe that wouldn't leave a seasoned Beaver bush pilot wishing for their old Beaver back?
In all of the time since that plane was designed, has something else has been designed and continues to be manufactured that can be called an upgrade without getting "bigger"? IE, has:

floats
a shorter or the same takeoff and landing roll at the Beaver's
max useful payload
the same or less stall speed with fully extended flaps
a same or less wingspan (negotiable if it's within 2 or 3 feet)

The motivation for the question is that less than 10 years ago, I remember a float plane flight out of Juneau, AK that I was on was flown by a Beaver still running a radial engine. I was amazed that something designed so long ago was still apparently considered  the "best" option for that carrier. Of course, the Beaver is now one of my favorite airplanes, but I am still amazed by the challenge it must be to find parts and maintain an aircraft of that age in the corrosive saltwater environment of SE Alaska.

As an ex DeHavilland employee I'll admit I'm a bit biased, but I'd say there isn't really a "direct" replacement so far.  Two reasons:
The Beaver was designed in Canada around a bush operator survey.  Outside Canada (and to a smaller extent Alaska), "bush operation" generally means remote land operations into dirt strips.  In Canada, "bush operation" meant almost exclusively seaplane operations, (and to a lesser extent ski operations in winter).  The survey provided the Dehavilland Canada designers with a wish list of features provided by seaplane operators running Norsemans and the like (sadly, helicopters and gravel strips to provide land plane access remote areas have replaced most seaplane use as basic transportation, and today most seaplane operations in Canada and Alaska support the tourist trade).
So, unlike its modern contemporaries, it is specifically designed to operate on floats, and is optimized for being serviced and loaded from a dock.  The fuel tanks in the belly, the placement and shape of the main doors, the battery location, etc. Easy to load, easy to service from a dock.  The Beaver's modern contemporaries aren't optimized for float operations quite the same way so the "fit" isn't quite as good for a seaplane operator. On the flying side, the very long wings and full span slotted flaps (the ailerons droop with the flaps) allows it haul loads out of very small lakes, with a decent rate of climb.
The other big reason is the engine.  The R-985 is one of the only large piston engines over 400 hp that is still commercially viable, that is, it's still feasible to keep running reliably in a commercial operation.  A piston engine is far cheaper to operate than a turbine.  Bush operators operate on very thin margins and direct operating costs have a direct impact on viability of an operation, so turbines are out of reach for most.
With the Petersen Mogas STC you can run an R-985 on aviation automotive fuel (Mogas) (like all 80 octane engines it's much happier on Mogas than 100LL), and in Canada at least some bush operators do this (the operator I worked for in the early 90s switched to Mogas when the supply of 80 octane in Canada dried up - 80 was still in production in Canada for some time after it disappeared in the US in the 1980s).
Add in the overall reliability of the design and ease of repair, and there you go.
The Beaver is kind of a single engine version of the DC-3. Its combination of features came together so well that after nearly 75 years, it's still the best choice for commercial seaplane operators to use as a business tool to make money. On top of that, it benefited from a large military order by the US Army that took roughly half of total production, 970 units, which has kept up the supply of used aircraft to keep prices in check (the story of the Army's adoption of the Beaver followed a trip to Alaska in the company demonstrator to take some generals fishing, and included a bizarre flyoff against a range of ill-suited contemporaries after US manufacturers complained about foreign sourcing - get the book the DeHavilland Canada Story for an interesting read).

Define "replacement".
Many operators have simply upgraded Beaver airframes to turboprop powerplants. For example, Kenmore Air Harbor in Washington State has a number of turbine Beavers (and Otters) and this has made the airframes worth keeping up, minimizing the need to literally replace with any other type. They do serve as "replacements" for the original radial-engined models.
That said, there are a number of other options currently manufactured that have similar characteristics and capabilities:

Cessna Caravan
Pilatus PC-6
Daher Kodiak
Sherpa

To name a few. These all have similar load capacity, can all be fitted with floats, and most have cabins about the same size as a Beaver's.
Regarding this part of your update to the question…

I am still amazed by the challenge it must be to find parts and maintain an aircraft of that age in the corrosive saltwater environment of SE Alaska.

It is a challenge. But as long as there are companies like Kenmore Air Harbor (notable in the industry for their decades-long on-going commitment to the type), and Viking Air (current holder of the type certificates for the out-of-production de Havilland types), even the radial-engined models can be kept flying. Engine parts are the biggest issue; floats are still in production and a variety of models can be used on the planes, avionics can be upgraded as needed, and airframe parts can be fabricated as needed from raw stock, for the most part, if spares are not readily available for purchase. Viking has a "spares support" business that can provide new parts in many cases.
Converting a Beaver to turboprop greatly simplifies maintenance, by replacing the component with the largest number of hard- or impossible-to-find parts with an in-production powerplant.
Frankly, the age of an aircraft is not nearly the impediment that most people probably think. There are challenges, to be sure. But even as expensive as it can be to keep an aircraft flying, it's even more expensive to buy a whole new one. And because aircraft are maintained to a higher standard in the first place, they can have a much longer life-time than what people outside the aviation industry might expect (cars might typically be operated for a decade, while typical aircraft can be safely operated for half a century or more, no problem). In that environment, there are a number of people and organizations dedicated to providing support for the aging fleet (such as Kenmore and Viking), and for them it's just "business as usual".


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Why do aircraft use 400 Hz AC instead of the 50 or 60 Hz of wall outlets?
Large aircraft electrical systems usually use 400 Hz alternating current (AC), while common household electrical outlets deliver AC at 50 or 60 Hz.  Why the difference?

The first question is NOT a duplicate question, although the answer to this IS addressed in one of the ANSWERS there. The second question IS a duplicate question, although the answer there is terrible, and neither one shows up when looking for "400 Hz" as a search. If I were searching for the answer to 400 Hz vs 60 Hz, "Why do airplanes use AC" wouldn't be an obvious place to look for the answer.

@RalphJ Still, now that you know, since you self-answered, the appropriate next action would be to first improve that second question with an edit to make it more searchable, then to post your answer there. Furthermore, if you can find a way to make that 2nd link not be a dupe of the 1st (which it is currently marked as), you could find a way to reopen it, thus allowing you to add your answer there. Or if you can find a way to add your answer to the 1st link (currently open), that works too.

@JasonC, the first question is perfectly fine as is, but it is fundamentally a different question than this one. For the second question to be marked as a duplicate of the first was absolutely a mistake, IMHO -- "why do acft use AC power not DC power" and "why do aircraft use 400Hz not 60Hz AC" are NOT the same question. You're right, I could edit the second question (which currently has a single, incorrect, answer) to try to get it reopened, and then post this answer to it, but THIS question is more findable in search & lacks the incorrect answer. JMHO.

@RalphJ Hm, well, it seems responsible to do something, no matter what that something is. We could perhaps petition a mod to re-close that second question as a dupe of this one, or merge them. There is no doubt that your Q & A are the better of the two.

Actually, one of the answers to the first question is the answer to this one (as I pointed out in my original comment, which has since been deleted).  That's also why the second question (which doesn't really have a valid answer to the question which was asked) has the first question as its' duplicate.  See this answer which addresses your question: http://aviation.stackexchange.com/a/3108/69  (Keep in mind that the reason we keep questions like this around when there is a duplicate is sometimes they are hard to find and this acts as a "sign post" for others.)

Note also that the description for the duplicate which was incorporated into your answer doesn't say that it is a duplicate question.  It says "This question already has an answer here:"....  As it stands now, using the second question as a duplicate is a bit recursive since it just points to the first one.  That being said, the system for duplicates exists because the Q&A that covers the duplicate isn't always obvious.

Induction motors turn at a speed proportional to frequency, so a high frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft (and ships). Transformers can be made smaller because the magnetic core can be much smaller for the same power level.  Thus, a United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power.
So why not use 400 Hz everywhere? Such high frequencies cannot be economically transmitted long distances, since the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.
Source
Further discussion of aircraft electrical systems
Further, further discussion of aircraft electrical systems
Added: cool discussion of the use of 400hz with Cray supercomputers on another S.E. forum

Marine vessels (military, not civilian) usually have 400 Hz as well. Same reason.

A bit OT from 50+ years ago in Norway... When melting aluminum with electrolysis it's beneficial with AC-power with a low frequency - which of course would be supplied by a local power-plant.  However the small towns often built around such smelters would get their power from the same plant...  And with AC-frequency of maybe just 10-30 Hz, that meant flickering lights and extra large transformers (because of the iron required) in appliances.  Higher frequency so you could use less iron, makes much more sense!

Inductors and transformers at 50 Hz are much larger and heavier than the 400 Hz case.
Aviation likes small weights.


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How does changing the altimeter setting in the US and elsewhere compare?
I have been trying to track down an answer to this question and I stumbled upon this website. Apologies if this answer is already out there. I have seen the FAR regulation, 14 CFR 91.121 - Altimeter settings. Is it possible for an ATC controller in the US to give you "Descend and maintain 18,000' (Not FL180)" and thus you would need to change your altimeter setting to local upon reaching?
I also fly ICAO quite often and the same question would apply to the transition level. Could a controller give you, as example, FL150 is transition lvl and 13,000 is transition altitude, "descend and maintain 15,000'." Would you set the local altimeter once level at 15 or wait until cleared to descend below? The source I was looking for ICAO procedures was the ICAO 8168, PANS-OPS, Volume I.
My understanding is that you do not change your altimeter setting until you are cleared below the transition level. I hope my questions aren't too confusing. I appreciate any clarification.


text:
Boeing 787 type rating
How tough/easy is to crack a 787 type rating course? Is a wide body aircraft difficult to fly especially when you are transitioning from 737? Any tips/suggestions would be much appreciated.

Welcome! Some will say it was difficult, others it was easy. Perhaps asking how long it takes for a B737 pilot to transition to a B787 would be a good start. If so edit your question.

I really can't imagine that for somebody who has a type in a 737 and has been flying it recently, the 787 course would be hard to pass. Having gotten the 737 type, you know how to study for a type & you understand how Boeing does things.  Do the work, memorize what needs to be memorized, study for the oral, pay attention in the sim, and you'll probably do just fine.  Boeing doesn't build their type rating courses as weed-out checkrides; they intend for their students to pass. I've never heard the 777 nor 787 characterized as hard to understand or hard to fly - quite the opposite, actually.

Biggest things here are going to be the availability of training courses as well as full motion simulators to do the training in. There are a lot of FMS systems for 737 aircraft operated by multiple companies offering type ratings in that airplane.  Conversely I only know of a few companies that offer initial and recurrent type rating work in a 787.   Boeing offers a type rating course in this aircraft, and as well as the individual 787 operators have their own initial and recurrent type rating training.
Your ease of obtaining a type rating is largely going to be a function of how big your bank account is.  You will also have to select whether you want to receive an initial type rating as a first officer on 787 or as a captain of the 787.  The training will probably take 3-4 weeks and approximately 20 to 30 hours of sim time (you will never fly the real thing for a type rating) to complete in a full motion simulator, and those are costing roughly 1000 dollars an hour to operate.   So at that time requirement plus say 2000 dollars for the course cost of materials,  you're probably looking at around 22,000-32,000 USD, provided of course you pass the check ride at the end.   If you were new to jets or other fast movers, this would probably be a monumental task for you.  If you have been type rated already in another airplane like the 737 or similar, the process should not be very difficult.
On top of that, unless you're going to go immediately fly for a 787 operator somewhere, that type rating is pretty much useless. (If you don't already have 4000 hours TT plus at least 1500 PIC Jet time, don't even bother applying; no airline would hire you for that role, type rated on the jet or not).  And it's only good for 12 months; you'll then be required to undergo a recurrent type rating as either a first officer captain on the 787 and will cost about 60% what the initial type rating did.


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Is it possible for me to work at NASA or other research companies as aircraft mechanic?
I know NASA is huge but is it possible for me to work there or other companies similar to it?  If possible, how?
I currently work at an MRO as aircraft mechanic. My work is mainly on flight controls. The only aircraft that I have experience on is a320 family.
We do some structural works too, knowledgable to SRM.
I'm from Philippines btw.

I'm not sure what you're asking. If NASA advertises for a mechanic and you meet their requirements - including being able to work legally at their location and perhaps needing a security clearance - then you can certainly apply.

Probably not, unless you are a U.S. citizen (dual-citizenship should be ok.) According to NASA,

Other than under extremely rare exceptions, you must be a U.S. citizen in order to work for NASA as a civil service employee.

It's extremely unusual for non-citizens to be able to work in the U.S. in agencies like NASA or the Department of Defense, where there is necessarily lots of equipment and/or information subject to ITAR controls and/or which is classified. This will generally also be true for contractor positions.
At my present job, we are not allowed to disclose anything more than high-level marketing material regarding products subject to ITAR to anyone who is not a U.S. citizen, for example, even though we don't make weapons or anything like weapons.

Thanks! I think I'm asking the wrong question lol. Is there any area which I can work not in commercial aviation? Field of aviation where revenue is not the priority? Just looking for other options.

Boeing, Airbus, Textron Aviation, and more are all major aircraft manufacturers and there are also many other aircraft part manufacturers such as GE. Also just to correct, NASA is not a company and is instead a government agency. Especially around the US, mechanics and pilots in the next 20 years are a major necessity as the frequency of air travel increases. Also, be reminded, working for the biggest companies will be less flexible than smaller ones. Now if there is a mechanic opening at NASA which there most likely is, be not afraid to take it.


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If cabin lights are dimmed during night landing so that your eyes will get used to the darkness, why do they let you use the reading lights?
Everytime the question of "why do they dim the lights during night landings" pops up, people say that it's to make passengers' eyes used to the darkness if an evacuation is needed (see: Why are the lights inside commercial airplanes turned off during take off and landing?)
However, on every commercial flight I've taken, the flight personnel always makes sure to mention that you can use the reading lights above you if you want, which are powerful enough to compromise your night vision (and that of people sitting next to you).
If the motivation is safety, why don't they disable these too? If anything, they should not be encouraging their use.

related(ish): https://skeptics.stackexchange.com/questions/8849/why-do-we-open-the-window-shades-during-landing-and-take-off

That is a good question. It is most likely a compromise. Turning down the cabin lights allows for night vision adaptation for most. Its better to have at least some of the passengers adapted, than none at all. Its a compromise between optimal safety (night vision adaptation) vs customer service (being able to finish reading your Harry Potter book).

We see similar types of compromises with portable electronic devices. If they are so dangerous (i.e. electronic interferences, distracted passengers, etc), then why are they allowed in the cabin at all? Flight attendants can't really ensure that they are all turned off or in Airplane mode, but forcing passengers to check all PEDs would result in a lot of unhappy passengers.


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How does a jet's throttle actually work?
How does a jet's throttle actually work? What does it do to the pressure chamber and the fire output controller?

You may restrict your question to a specifi generation of jet engines. Depending of the control law, you may not control the same physical quantity (N1 rpm, total thrust, fuel flow,...). Nowadays, this is controlled by the fadec, but it was different in the past.

I'd suggest that you review the topic of how a jet engine works, first, and then review how a jet engine fuel control unit works as it doesn't sound like you're very familiar with engine components; I've never heard of a 'pressure chamber' or 'fire output controller'.
Modern jet aircraft technically don't use throttles; rather they are equipped with thrust levers which are connected to a Fuel Control Unit (FCU).  This can come in the form of a mechanical computer in the case of earlier engines or a digital electronic computer called a Fully Authority Digital Engine Controller (FADEC), similar to the schematic in aeroalias's answer for the F100 fighter engine installation on the F-16 airplane.
Early jet aircraft did use a throttle - literally a cockpit lever connected to a throttleable valve to precisely meter fuel into the combustion chamber(s) of the engine.  This could be problematic to operate in flight as the fuel rate has to be changed as altitude - and consequently combustor inlet conditions - changes, making the engine vulnerable to flameouts from excessively rich fuel flow and compressor stalls from abrupt throttle changes.  FCUs were developed, specific to each engine to offer simplified control.

The throttle (or thrust lever) in a gas turbine engine adjusts the thrust produced by controlling the fuel flow to the combustion chamber.
Most of the modern engines are actually controlled by the Full Authority Digital Engine (or electronics) Control, FADEC (or Engine Control unit)- so the signals from the throttle are sent to the computer, which regulates the fuel flow based on various parameters (including engine safety) thereby adjusting thrust. The computer handles the additional components of the engines like the thrust reversers and afterburners.
The image below shows the throttle controlling the fuel system through the engine control in the Pratt & Whitney F100 engine that powers F-15 and F-16.

Image from kaskus.co.id

Worth noting that jet engines, by nature, always run lean once started - there is always leftover oxygen that can burn more fuel (this is how afterburners work).  As such, adding fuel flow at any point will cause more combustion and the engine will spin faster - ingesting more air, making more available for combustion, etc.  Fundamentally, to answer OP's question, the flow of fuel is largely all that needs to change to alter the operating speed (and power) of a jet engine.

So, it boils down to "just like diesel".

Jet engines run on the Brayton cycle which is isobaric (constant pressure) combustion from a thermodynamic perspective.
Assuming the engine is already in a steady state, when you open the throttle you introduce more fuel (regardless of how computerised or otherwise).
More fuel translates as more heat into the combustion chamber.  As we calculate this as constant pressure this mean we increase the volume of the fluid flowing through.  In practice this is seen as a faster fluid flow rate exiting the chambers
This increased volume/flow rate impinges on the turbine as it expands adiabatically it imparts more work into the turbine, spinning it quicker which spins the compressor quicker drawing in more airflow.
Once past the turbine the exiting gas flow has a higher velocity and higher momentum which through Newtons laws becomes greater thrust.
It's not finished there through.  The turbine/compressor will continue to speed up (adding more air to the system) until the system achieves a new steady state at a higher fuel flow, higher compressor/turbine rotation speed, higher turbine temperature and of course higher thrust.
We could keep adding higher and higher fuel flows but there are a number of limits to the system, which ultimately limits the maximum thrust.


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Why can't helicopters fly at high altitudes?
I recently watched a movie and in the movie it stated that the helicopter could not fly to the top of mt.everest to rescue the person stuck on the top. So why can't helicopters fly at such high altitudes?

Ask yourself this: Could a helicopter fly in a vacuum? Certainly not. So somewhere between sea level and outer space a helicopter is going to be unable to ascend further due to lack of air pressure. Where exactly that point is depends on the design characteristics of each model of helicopter.

Actually this has been done on a AS350 B3, but this is exceptional, and was only a flight test. The highest rescue was by the same helicopter on the Annapurna (6,900 m - 22,640 ft). See Wikipedia.

This doesn't look like a duplicate. The other question asks for a technical term, while this one asks why helicopters have a certain limitation. I agree they are related, but they are not the same.

Don't believe everything you see in the movies. Doubly so if the movie originated in Hollywood.
The world altitude record for a helicopter is 40,814ft (12440m), some 11,000 feet (3353m) higher then Everest, set in 1972 Reference: Wikipedia
In 2005 Didier DelSalle famously touched down on the summit of Everest in an AS350 Squirrel Reference: Wikipedia. See below for a video.
Both feats involved specially prepared aircraft and highly experienced crew.

As has already been pointed out, a helicopter, just like any other aircraft, has a ceiling above which they cannot fly. Since it's clear that it is possible to fly helicopters to the required altitude in certain conditions, this is just a red herring.
The real reason helicopters don't routinely fly to those altitudes is that they're not designed to. As with everything in aviation, performance is a trade off between engineering, aerodynamics and commercial pressures.
There's a big market for helicopters that can fly up to, say, 12-15,000ft (3600-4500m). The market for helicopters capable of rescuing climbers from the top of Everest is, at best, limited, and the technical demands of building a craft routinely capable of such a flight will push the costs up dramatically.
In short, they don't because nobody will pay for it.

I think another factor is that weather conditions have to be ideal for a flight to that altitude. The typical rescue is unlikely to be in ideal weather conditions.

Technically, someone can install rockets onto a helicopter then it can even go into space, but that's just a stupid machine and nobody will fund it.

@Nelson for an IRL AirWolf? TAKE MY MONEY ALREADY!!!

@Burgi Your money isn't going to be enough...

The helicopter flies as long as the blades produce lift. Now,the lift is proportional to the density at a particular altitude. However, as altitude increases, the density goes down.
Usually, the helicopter compensates for this by increasing the lift coefficient by increasing the blade pitch (as the blade rotational speed, and hence V is constant). However, at a certain altitude, the maximum lift coefficient of the blades is reached and no further increase in lift is possible.
Hence, the helicopter cannot fly beyond this altitude. This is the absolute ceiling of the helicopter.

In most helicopters, the drag will exceed the available (or at least rated) power output of the engine leading to RRPM droop before max lift is reached.

A deficiency I see in this answer is the same is true for planes.  Planes need air for their wings to work too.  Why helicopters need more air than planes is the real and interesting question.

@leorleor my guess would be the difference in surface area of a wing on a fixed wing plane vs the surface area of the blades on a helicopter main rotor make the difference between planes and helicopters.  There's also the limit of the rotational speed of the engine (or motor) spinning the blades on a copter (tortional forces to be contended with and need for balance and ability allow blades to flap when advancing or retreating to keep lift on each side constant).  Basically like others say the cost doesn't outweigh the benefit for use case of helicopters.

Also helicopters don't maintain their forward momentum typically (they are stopping and going with regard to x/y coordinates) whereas a plane has inertia in the direction the jets are driving the plane and it is relatively continuous in direction and speed (stopping and going is a big "waste"/use of energy).  Helicopters are good at short distance precision control and lifting power, but not good for long range or high altitude, it's just a trade off in the design, form = function.


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Are Aircraft yokes self centering in non-auto pilot mode?
In a typical car steering wheel if you release it while the car is in motion, it will return to its center, neutral position.
What's the corresponding situation in an airplane? Is a yoke self centering? Or does it stay put until corrected by the pilot inputs? Let's stick to non autopilot modes to simplify the basic behavior.
The forces on the control surfaces ought to be high when deflected from their default position, right? So I'm assuming that offers a restoring torque? E.g. with the rudder if you take your feet off the pedals then it centers, I think.
Some additional points:

As a simplified case what happens on the ground when the aircraft is stationary. If I deflect the control surfaces to their extreme position & release the yoke would they all return to the neutral position? Is the restoring force gravity or spring loading?
The answers on the other question seem to focus on ailerons but what about elevators?
Does the rudder typically self center with more alacrity than the other surfaces? Why?

This depends on the roll stability of the airplane.  For many there will be a correcting force below some bank angle and a diverging force above some bank angle with a neutral regime between.

@Simon: Indeed. It looks a duplicate. What's the right protocol to close my question? Just to delete it?

Several folks will stop by and vote to close. It is usually considered a Good Thing™ at SE to leave the newly duplicate questions as a sign-post to the 'original' - if you didn't find the original, odds are good others won't either. This is one more opportunity for someone to find it instead of asking yet another duplicate.

@curious_cat: It may not be a duplicate. There are two things: whether the stick centres itself (yes, it does, for suitable, and relatively complicated, definition of centre) and whether the aircraft returns to flying straight (no, it does not). That suggested duplicate question addresses the later only. The former would still make a good question with potentially quite long answer detailing the definition of centre and what it means.

@JanHudec: Great. You are right. I am looking forward to some good answers about this.

With respect to "centering", a yoke only "centers" itself in the equilibrium point where forces on both ailerons and on both top and bottom of the elevator/stabilator are equal. That said, I wouldn't want to let the yoke "center and fly itself" as the forces on the control surfaces can be equal even when the aircraft is not straight and level. If not enough power is applied the plane will pitch down and "center" as you say, and if too much power is applied the plane will pitch up and then "center". As for roll, I find that in light aircraft (Cirrus excluded as the side stick has a spring mechanism) you don't usually want to leave the yoke out of hand as slight wind and light wind shear will cause the airplane to roll somewhat. So - short answer is - yes, it will "center" eventually but you might not like the attitude the plane is in when it's done, much of this depending on power setting and gusts/shear aloft/turbulence. As for autopilot, a roll and pitch (2-axis) autopilot actually continually applies force to the controls to keep the airplane level or turning as commanded, and at a constant altitude or climb/descent/airspeed as commanded, so I wouldn't say the controls really "center" when on autopilot either. Cheers!
As a bit more of an explanation, a "nice" airplane (one with positive aerodynamic stability) with the appropriate power setting should re-enter and maintain straight and level flight if the controls are disturbed and the yoke is released (but I've always had to input a little roll to keep the wings level). Check out the following picture from the FAA Pilot's Handbook of Aeronautical Knowledge Page 4-14:

Notice that the orange line eventually gets more and more flat. You can expect that in a Cessna 172 or something of the like... not in a more aggressive plan like aerobatic planes and fighter jets - you'll see something a little more like the green or red line. You can read more in Chapter 4 of the FAA PHAK (link here).

By your explanation, gliders should self-center, but I can tell you from experience, gliders are no better than airplanes.


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Why did the flight Osaka -> Frankfurt circle above the airport after taking off from Osaka International?
When departing form Osaka International (KIX) the Osaka city passed below twice, the second time much lower. Looks like our 747-400 was circling up in spiral before heading a long way over Russia to Europe.
I understand the reason of flying in circles before landing (holding pattern, waiting in a queue for landing). But why circle over the airport of departure? I think it could be more economical and faster to pick the altitude while heading in a needed direction. Is there also a queue to leave the airport? Why not to wait on the ground then?
If was the flight LH741 (Osaka - Frankfurt), departing 24.10.2017, 10:00 from Terminal 1.

Have a look at the airport charts: Some SIDs (Standard Instrument Departure) mandate circling.

Sometimes circling patterns are flown while climbing after departure in order to gain altitude before setting course across terrain or restricted airspace (although probably much more often for terrain).

Related, maybe a dupe? It's a different airport, but the same basic question.

NANKO ONE Departure
The NANKO ONE Departure, as already written by Robᵩ, is one of the most used departures out of KIX/RJBB.
The unusual design with the climbing pattern over the bay is used to minimize interference with the traffic in and out ITM/RJOO Osaka International Airport also known as Itami Airport in the north of the city and to reduce noise over populated areas. But let me explain in detail:
Geographic situation and airports

Screenshot from https://skyvector.com
The Osaka Bay area is densely populated and served by numerous airports, airfields and helipads. For your question we concentrate on the following four airports:
The area has two large airports:

KIX/RJBB Kansai International Airport

177,109 aircraft movements (2016)
~25.3 million passengers (2016)

ITM/RJOO Osaka International Airport aka Itami Airport

139,630 aircraft movements (2015)
~14.6 million passengers (2015)

and two smaller ones:

UKB/RJBE Kobe Airport

27,468 aircraft movements (2015)
~2.4 million passengers (2015)

none/RJOY Yao Airport

airbase for the Japan Ground Self-Defense Force
also used by general aviation
no numbers published

Runway layout and ATC considerations
You might have noticed that the runway systems of KIX and ITM are perpendicular to one another. Kobe and Yao have runways parallel to each other but at a 45 degree angle to KIX and ITM. This poses a problem with arriving and departing traffic to all four airports.
Westerly wind direction
Think of wind from westerly directions. In this case ITM uses RWY32L/R und KIX uses RWY24L/R. Normally you line up the arriving traffic on the runway centerline about 15-20NM out. Keeping this in mind the arriving aircraft will cross their path somewhere in the east of Osaka. Additionally UKB will use RWY27 and their arriving traffic is crossing the path of the two others as well. Add Yao (RJOY) departures on RWY27 into the mix and you have a nightmare ATC-wise sorting and spacing the traffic to avoid separation conflicts. This reduces the capacity of all involved airports as the spacing between arriving flights has to be bigger to accommodate for arriving (and departing) flights of the other airports.
Easterly wind direction
Now to your case - departures with easterly winds. In these conditions KIX uses RWY06L/R as you did on your flight. ITM will use RWY14L/R. If both airports used straight out departures you have a crossing situation similar to the arrivals with westerly winds. Add Kobe (UKB) using RWY09 to the mix and you have three departure routes crossing. To add some flavor for the controller there might be an arrival into Yao (RJOY) RWY 09. Another ATC nightmare.
Noise
The described situations above are all based on hypothetic straight out departures and arrivals. You surely know that, as a rule of thumb, an aircraft makes more noise the higher the flap setting. Departures and arrivals over populated areas introduce a lot of unwanted noise into local communities. This is therefore something to be avoided.
Sophisticated airspace layout
A solution to most of the problems described above lies in the unusual airspace and departure/arrival procedure design. Lets have a look at the KIX arrivals first:

Cropped from the Japanese AIP RJBB AD2.17 Positive Control Area
The image shows the final approach for both directions. RWY06L/R is rather straight forward. From TOMOH straight on the centerline all the way down to the runway. RWY14L/R is a different beast. At MAYAH you are far from aligned with the runway centerline. You are basically flying in the wrong direction. But it avoids Kobe (UKB) neatly and stays clear from the ITM area further north-east. Additionally it keeps the noisy aircraft (flaps and gear extended) over the water.

Cropped from the Japanese AIP RJBB AD2.17 Terminal Control Area and colored by me.
I highlighted the relevant KIX airspace in blue and the ITM airspace in green. You can imagine the "funnels" to guide the traffic in and out of the airports. This way you have the traffic for both airports separated.
But whats about departures to the north-east like your Lufthansa flight? You need to cross the path of the traffic of the other airport somewhere. Here, the magic sauce is vertical separation. Just keep one traffic flow way higher than the other and you avoid the need to separate them from each other manually. The straight line distance from the runway in KIX to NANKO is too short to reach the required altitude to stay clear of the other traffic. That is basically the reason for that "circle" you flew on departure.

Cropped from the Japanese AIP RJBB AD2.24-SID-19
It extends the mileage to NANKO so the aircraft can reach a higher altitude at that waypoint. Additionally the flap retraction is kept over the Osaka Bay, the aircraft crosses the shoreline at an higher altitude and noise over populated areas is minimized. Pretty clever in my eyes.
I hope this explains it in more depth - feel free to ask for clarification.
Cheers,
Chris

Looking at FlightAware, we see this takeoff for your flight:

Examining some airport charts for KIX, this looks like the standard departure NANKO REVERSAL THREE DEPARTURE from runway 06R.

I guess that the loop is to give the aircraft enough time to climb to 8000 before it reaches NANKO. And, I guess the 8000 feet is for either terrain or noise abatement (notice the climbing loop is entirely over water.)

The crossing restriction may be also to separate traffic from the other Osaka International Airport, RJOO/ITM, which is almost in the way.

There's also Kobe Airport (RJBE) visible in the last chart as an island on the north end of the bay.

The reason is to keep you over the water in the climb for noise abatement for the city. Japan is very noise sensitive. You climb to get higher over the water at high power settings before going over land. Hence you are at a higher altitude which equals less noise for the city.